Interpretive Summary: The main source of beef carcass contamination during processing has been identified as the hide. Transportation from the feedlot and temporary holding at the processing plant have been identified as potential sources of E. coli O157:H7 and Salmonella hide contamination. The objective of this study was to perform a comprehensive tracking analysis of E. coli O157:H7 and Salmonella associated with beef cattle from the feedlot through processing. Cattle were sampled in a feedlot then transported in multiple lots to three large, commercial, fed beef processing plants in the United States. Pathogen prevalence on cattle hides increased on every lot of cattle between exiting the feedlot and beginning processing. Prior to loading cattle, E. coli O157:H7 was found in 64% of the trucks. E. coli O157:H7 was detected in over 60% of the samples from each lairage environment area, while Salmonella was detected in over 70% of the samples from each lairage environment area. E. coli O157:H7 and Salmonella isolates were tracked by comparing the DNA profiles of isolates collected before and after transport. The results of the tracking indicate that the transfer of bacteria onto cattle hides that occurs in the holding environments of U.S beef processing plants accounts for a larger proportion of the hide and carcass contamination than does the initial bacterial population found on the cattle exiting the feedlot. Finally, the results of this study indicate that hide wash cabinets are effective in removing contamination derived from the lairage environment.

Technical Abstract:
The main source of beef carcass contamination during processing has been identified as the hide. Transportation from the feedlot and lairage at the processing plant have been identified as potential sources of E. coli O157:H7 and Salmonella hide contamination. The objective of this study was to perform a comprehensive tracking analysis of E. coli O157:H7 and Salmonella associated with beef cattle from the feedlot through processing. Cattle (n=581) were sampled in a feedlot then transported in multiple lots to three large, commercial, fed beef processing plants in the United States. Pathogen prevalence on cattle hides increased on every lot of cattle between exiting the feedlot and beginning processing. Prior to loading cattle, E. coli O157:H7 was found in 9 of 14 (64%) trucks. E. coli O157:H7 was detected in over 60% of the samples from each lairage environment area, while Salmonella was detected in over 70% of the samples from each lairage environment area. E. coli O157:H7 and Salmonella isolates (n = 3,645) were analyzed using PFGE. The results of the PFGE tracking indicate that the transfer of bacteria onto cattle hides that occurs in the lairage environments of U.S beef processing plants accounts for a larger proportion of the hide and carcass contamination than does the initial bacterial population found on the cattle exiting the feedlot. Finally, the results of this study indicate that hide wash cabinets are effective in removing contamination derived from the lairage environment.